The present invention relates generally to Magnetic Resonance Imaging (MRI) systems, and more particularly, to a method and system for reducing cryogen consumption in MRI systems.
Magnetic Resonance Imaging (MRI) is a well-known medical procedure for obtaining detailed, one, two and three-dimensional images of patients, using the methodology of nuclear magnetic resonance (NMR). MRI is well suited to the visualization of soft tissues and is primarily used for diagnosing disease pathologies and internal injuries.
Typical MRI systems include a super conducting magnet capable of producing a strong, homogenous magnetic field around a patient or portion of the patient; a radio frequency (RF) transmitter and receiver system, including transmitter and receiver coils, also surrounding or impinging upon a portion of the patient; a gradient coil system also surrounding a portion of the patient; and a computer processing/imaging system, receiving the signals from the receiver coil and processing the signals into interpretable data, such as visual images.
The super conducting magnet is used in conjunction with a gradient coil assembly, which is temporally pulsed to generate a sequence of controlled gradients in the main magnetic field during a MRI data gathering sequence. Inasmuch as the main superconducting magnet produces a homogeneous field, no spatial property varies from location to location within the space bathed by such field; therefore, no spatial information, particularly pertaining to an image, can be extracted therefrom, save by the introduction of ancillary means for causing spatial (and temporal) variations in the field strength. This function is fulfilled by the above-mentioned gradient coil assembly; and it is by this means of manipulating the gradient fields that spatial information is typically encoded.
Super conducting magnets operate under extremely low temperatures. This is commonly accomplished through the use of cryogens such as liquid helium. The cryogens must often be stored and delivered under low temperatures in order to deliver the proper efficiency. Cryogens such as liquid helium, however, are not abundant and therefore can significantly impact the cost of operation of the MRI system. In addition exposure of liquid helium to room temperature magnets can result in the boiling of the liquid helium which negatively impacts the performance and efficiency of the MRI system.
It is known that the economics and efficiency of cryogen based MRI systems can be improved by cooling the MR magnet components from room temperature to an intermediate temperature closer to the final liquid helium operational temperatures. Pre-cooling the MR magnet components is preferably accomplished through low cost and easily available cryogen materials. Existing pre-cooling designs operate under thermodynamic inefficiencies that consume more refrigerant/cryogen. This emphasizes the cost components of liquid helium systems. Additionally, the inefficiencies can result in the generation of undesired condensate/icing. This can result in the freezing and seizing of the blower bearings. The blowers and bearings may be redesigned in order to minimize the impact of bearing freeze. This, however, requires the use of special blowers that increases both the initial cost of the MRI system as well as the cost of maintenance and replacement blowers.
It would, therefore, be highly desirable to have a MRI cooling assembly with improved cooling efficiency and a reduction of cryogen consumption. It would additionally be highly desirable to have a MRI cooling assembly that could be implemented without the necessity of costly specialized blower assemblies.